NEW DEVELOPMENTS IN OPTICAL PROFILING AND SAMPLING SYSTEMS FOR THE STUDY OF MARINE SNOW AND RELATED MICROBIAL PROCESSES <B>NEW DEVELOPMENTS IN OPTICAL PROFILING AND SAMPLING SYSTEMS FOR THE STUDY OF MARINE SNOW AND RELATED MICROBIAL PROCESSES</B> <HR><P> Picheral, M. & Gorsky, G. <BR> CNRS, URA 716, Observatoire Oceanologique, B.P. 28, 06230 Villefranche sur mer, France. </B><P><P> The main scope of the ongoing MAST II, EMPS Project is the study of the role of suspended particulate matter on microbial activities. <P><P> Because of the fragility of suspended aggregates, non-destructive instruments such as the Underwater Video Profiler (UVP) are more appropriate for in situ abundance or size distribution estimations than collection by conventional techniques. The UVP system consists of an underwater unit and a powerful image processing system and is used for the quantitative study of suspended particles larger than 100 micrometer(s) from the surface to a depth of 1000 m. The image acquisition unit consists of 1) a Hi8 Sony video camera recorder, 2) an electronic control unit and data logger, 3) four 24 V batteries, 4) two exchangeable light sources, the first with a collimated light field of 19.2 x 14.3 x 1.5 cm in front of the camera to record particles > 100 micrometer(s) and the second to illuminate a volume of 100 l for zooplankton estimations, 5) a Seabird SBE-19 CTD. If the system is lowered at the speed of 1m /s, one image is recorded every 4 cm. One 0-1000 m vertical profile lasts 35 min deck to deck and contains 25000 images which are processed by a system composed of a) a real time image digitizer, b) a VTR, c) a PC and d) software. The detailed data processing takes 5 hours. The profile can be scanned and images with given pixel patches can be stored for macro-zooplankton recognition. <P><P> On board, the recorded profile is transferred via a waterproof connector to a computer, is digitised and a raw abundance profile of suspended particles is printed out 55 min after the commencement of the lowering. The consequent marine snow sampling strategy is then determined according to the UVP profile. The sampling is realised by a new cable operated open-close sampler called Programmable Detritus Sampler (PDS). This sampler was constructed in the framework of the MAST II EMPS Project and consists of a Plexiglas cylinder of 16.5 cm internal diameter with rotating waterproof taps at each end, electronic control unit, aluminium frame for cable and laboratory fixation. The rotating motor and the electronic control unit were constructed by the Technicap SA., France. The upper tap can be separately opened in the laboratory and the particles can be individually sampled, or gently concentrated for analyses.<P><P> The improvements of the new UVP generation realised with the support of the EMPS Project involve the use of: a) Chatwick synchronised strobe lights with IR cut-off filters, b) compact high resolution video camera placed in the centre of a c) plankton net equipped with a LHPR collector. The collimated light field is positioned in front of the net opening. <BR> This system will allow simultaneously: <P><P> *to collect quantitative data on SPM abundance and size distribution in the water column (from a size of 100 micrometer(s) to more than 10 cm) , <BR> * to estimate the vertical distribution of macrozooplankton and especially that of fragile gelatinous forms, important producers and consumers of suspended particulate matter <BR> * to sample the mesozooplankton,<BR> * to perform physical parameters data acquisition.<P><P>